Limp home operational mode for an electric vehicle

ABSTRACT

Methods and apparatus are provided for a limp home operational mode for an electric motor system. The method includes determining whether a resolver has failed. When the resolver has not failed, operation of the electric motor system uses resolver signals. When the resolver fails, operation of the electric motor system uses sensorless rotor position and rotor speed signals.

TECHNICAL FIELD

The present invention generally relates to electric motor systems forelectric and hybrid vehicles, and more particularly relates to a methodand apparatus for enabling a limp home operational mode in an electricmotor system for an electric or hybrid vehicle.

BACKGROUND OF THE INVENTION

Electric motor systems in electric or hybrid vehicles utilize a resolvercoupled to an electric motor system thereof to generate signalscorresponding to a position and a speed of a rotor of the electricmotor. When the resolver fails, however, the electric motor systemcannot provide position and speed signals necessary for control of theelectric motor system.

Accordingly, it is desirable to provide a method and apparatus for limphome operation that is operable when the resolver fails. Furthermore,other desirable features and characteristics of the present inventionwill become apparent from the subsequent detailed description and theappended claims, taken in conjunction with the accompanying drawings andthe foregoing technical field and background.

SUMMARY OF THE INVENTION

A limp home controller is provided for controlling operation of aninternal permanent magnet motor, the controller including a sensorlessspeed and position estimator and a signal selector. The sensorless speedand position estimator generates sensorless rotor position and rotorspeed signals. The signal selector is coupled to a resolver forreceiving sensed rotor position and rotor speed signals from theresolver and is coupled to the sensorless speed and position estimatorfor receiving the sensorless rotor position and rotor speed signalstherefrom. The signal selector determines whether the resolver hasfailed and provides the sensed rotor position and rotor speed signalsfor controlling the operation of the internal permanent magnet motorwhen the resolver has not failed and provides the sensorless rotorposition and rotor speed signals for controlling the operation of theinternal permanent magnet motor when the resolver has failed.

A method is provided for operation of an electric motor system. Themethod includes determining whether a resolver has failed and operatingthe electric motor system using resolver signals when the resolver hasnot failed, while operating the electric motor system using sensorlesssignals when the resolver has failed.

In addition, an electric motor system is provided. The electric motorsystem includes an internal permanent magnet motor, an inverter, aninverter controller, a resolver, and a limp home controller. Theinternal permanent magnet motor includes a plurality of phases and arotor. The inverter generates a plurality of phase signals in responseto modulated control signals and is coupled to the internal permanentmagnet motor for providing each of the plurality of phase signals to acorresponding one of the plurality of phases of the permanent magnetmotor. The inverter controller generates the modulated control signalsin response to a rotor position signal, a rotor speed signal and phasecurrent signals, the phase current signals corresponding to currents ofone or more of the plurality of phase signals. The resolver is coupledto the internal permanent magnet motor and senses a position andmovement of the rotor, the resolver generating sensed rotor position androtor speed signals in response to the position and the movement of therotor. And the limp home controller is coupled to the resolver fordetermining whether the resolver has failed and is coupled to theinverter controller for providing the sensed rotor position and rotorspeed signals to the inverter controller as the rotor position signaland the rotor speed signal when the resolver has not failed whileproviding sensorless rotor position and rotor speed signals generated bythe limp home controller to the inverter controller as the rotorposition signal and the rotor speed signal when the resolver has failed.

DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and

FIG. 1 illustrates a block diagram of an electric motor system inaccordance with an embodiment of the present invention;

FIG. 2 illustrates a block diagram of an inverter controller of theelectric motor system of FIG. 1 in accordance with the embodiment of thepresent invention;

FIG. 3 illustrates a block diagram of a limp home controller of theelectric motor system of FIG. 1 in accordance with the embodiment of thepresent invention;

FIG. 4 illustrates a block diagram of a sensorless position and speedestimator of the limp home controller of FIG. 3 in accordance with theembodiment of the present invention;

FIG. 5 illustrates modal operation of the sensorless position and speedestimator of FIG. 4 in accordance with the embodiment of the presentinvention; and

FIG. 6 illustrates a flow chart of the operation of a limp homecontroller of the electric motor system of FIG. 1 in accordance with theembodiment of the present invention.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, brief summary or the following detailed description.

Referring to FIG. 1, a block diagram of an electric motor system 100 inaccordance with an embodiment of the present invention includes athree-phase synchronous permanent magnet motor 102 operating undercontrol of an inverter 104 and an inverter controller 106. A resolver108 is mechanically coupled to a rotor shaft of the motor 102 andoutputs amplitude modulated sine and cosine waveforms sensed from therotation of the motor 102 to a resolver to digital conversion block 109.The resolver to digital conversion block 109 generates sensed rotorposition and rotor speed signals in response to the waveforms from theresolver 108. While the present embodiment includes a three-phasesynchronous internal permanent magnet motor 102, the electric motorsystem 100 may include permanent magnet motors of other designs wherethe sensed rotor position and rotor speed signals (θ_(sensed),ω_(sensed)) are generated in response to the position and the movementof the rotor of the motor 102.

The resolver to digital conversion block 109 is coupled to a limp homecontroller 110 and provides the sensed rotor position and rotor speedsignals thereto. In accordance with the present embodiment, the limphome controller 110 generates a rotor position signal, θ, and a rotorspeed signal, ω, in response to the sensed rotor position and rotorspeed signals.

The inverter 104 is coupled to a direct current (DC) source 112 andgenerates a plurality of phase signals in response to modulated controlsignals 114 received from the controller 106 coupled thereto. The numberof phase signals corresponds to the number of phases of the motor 102which, in the present embodiment, includes three phases. The inverter104 is coupled to the permanent magnet motor 102 and provides theplurality of phase signals on phase wires 116 for controlling theoperation of the permanent magnet motor 102.

The inverter controller 106 is coupled to the inverter 104 and generatesthe modulated control signals 112 in response to the rotor positionsignal, θ, the rotor speed signal, ω, a speed command signal, Speed*,provided from a higher level controller (not shown), and phase currentsignals (I_(a), I_(b), I_(c)) sensed from the phase wires 116. Theinverter controller 106 provides the modulated control signals 114 tothe inverter 104 for generation of the plurality of phase signals.

The inverter controller 106 provides two phase stationary framealpha/beta currents, I_(α) and I_(β), and two stationary frame voltagecommands, V*_(α) and V*_(β), to the limp home controller 110. The limphome controller 110, as described above, generates the rotor positionsignal, θ, and the rotor speed signal, ω, in response to the sensedrotor position and rotor speed signals (θ_(sensed), ω_(sensed)) from theresolver 108 and provides the rotor position the rotor speed signals, θ,ω, to the inverter controller 106. The limp home controller 110 alsogenerates two stationary frame injection voltage commands 118, V*_(α)_(—) _(inj) and V*_(β) _(—) _(inj), and provides the injection voltagecommands to the inverter controller 106 for operation of the motor 102at low speeds.

Referring to FIG. 2, an exemplary block diagram of the invertercontroller 106 includes a three to two transformation module 202 whichconverts the three sensed phase current signals (I_(a), I_(b), I_(c)) toequivalent two phase stationary frame alpha/beta currents, I_(α) andI_(β). The two phase alpha/beta currents, I_(α) and I_(β), are providedto a stationary to synchronous reference frame transformation module 204and the limp home controller 110 (FIG. 1). The stationary to synchronousreference frame transformation module 204 transforms the two phasealpha/beta currents I_(α) and I_(β) to synchronous frame feedbackcurrents, I_(qse) _(—) _(fb) and I_(dse) _(—) _(fb), in response to therotor position signal, θ. The synchronous frame feedback currents,I_(qse) _(—) _(fb) and I_(dse) _(—) _(fb), are provided to currentregulators 206 for generating stationary frame voltage commands, V*_(α)and V*_(β) in response to the rotor position signal, θ and two currentcommands in the synchronous reference frame, I*_(dse) and I*_(qse).

The speed command signal, Speed*, which, as described above, is providedfrom a higher level controller, is provided to a summer 208 whichsubtracts the rotor speed signal, ω, and provides the resultant errorsignal to a speed regulator module 210 which generates the torquecommand signal, T*_(e). The torque command signal, T*_(e), is providedto an optimal torque per ampere trajectory determination block 212 whichgenerates the two current commands in the synchronous reference frame,I*_(dse) and I*_(qse), for provision to the current regulators 206 inresponse to the torque command signal, T*_(e), the rotor speed signal,ω, and the DC link voltage, V_(DC).

Thus it can be seen that the stationary frame voltage commands, V*_(α)and V*_(β), are generated by the current regulators 206 by derivingvoltage command signals from a combination of the synchronous framecurrent commands, I*_(dse) and I*_(qse), and the synchronous framefeedback currents, I_(qse) _(—) _(fb) and I_(dse) _(—) _(fb), andtransforming the resultant voltage command signals to the stationaryframe voltage commands, V*_(α) and V*_(β), utilizing the rotor positionsignal, θ. The stationary frame voltage commands, V*_(α) and V*_(β), arecombined with injected voltage commands, V_(α) _(—) _(inject) and V_(β)_(—) _(inject) 118, at signal summers 214, 216 and the resultant signalsare provided to a two to three phase transformation and modulatedcontrol signal generator 218 which generates the modulated controlsignals for provision to switching elements of the inverter 104 (FIG.1).

Referring next to FIG. 3, an exemplary block diagram of the limp homecontroller 110 in accordance with the present embodiment includes asensorless rotor and speed estimator 302 and signal selector 304. Thesensorless rotor and speed estimator 302 receives two phase stationaryframe alpha/beta currents, I_(α) and I_(β), and stationary frame voltagecommands, V*_(α) and V*_(β), and generates sensorless rotor position androtor speed signals, θ_(sensorless) and ω_(sensorless), in response.

The signal selector 304 receives the sensorless rotor position and rotorspeed signals, θ_(sensorless) and ω_(sensorless), from the sensorlessrotor and speed estimator 302 and the sensed rotor position and rotorspeed signals, θ_(sensed), ω_(sensed), from the resolver 108 (FIG. 1).The sensed rotor position and rotor speed signals, θ_(sensed),ω_(sensed), are provided to a resolver failure detect module 306 and aselector 308. The resolver failure detect module 306 determines whetherthe resolver 108 has failed in response to the sensed rotor position androtor speed signals, θ_(sensed), ω_(sensed). A resolver 108 failure mayoccur when wires to the resolver fail, for example.

When the resolver failure detect module 306 determines that the resolverhas failed, the resolver failure detect module 306 generates a resolverfail signal and provides the resolver fail signal to the selector 308.The selector 308 receives sensorless rotor position and rotor speedsignals, θ_(sensorless) and ω_(sensorless), from the sensorless rotorand speed estimator 302 as well as the sensed rotor position and rotorspeed signals, θ_(sensed) and ω_(sensed), from the resolver 108. In theabsence of the resolver fail signal (the lack of the resolver failsignal indicating that the resolver 108 has not failed), the selector308 provides the sensed rotor position and rotor speed signals,θ_(sensed) and ω_(sensed), to the inverter controller 106 (FIG. 1) asthe rotor position signal, θ, and the rotor speed signal, w. On theother hand, when the selector 308 receives the resolver fail signalindicating that the resolver 108 has failed, the selector 308 providesthe sensorless rotor position and rotor speed signals, θ_(sensorless)and ω_(sensorless), to the inverter controller 106 (FIG. 1) as the rotorposition signal, θ, and the rotor speed signal, ω. In this manner, thelimp home controller 106 advantageously provides a limp home operationmode when the resolver 108 fails by generating sensorless rotor positionand rotor speed signals, θ_(sensorless) and ω_(sensorless), forprovision to the inverter controller 106 (FIG. 1) as the rotor positionsignal, θ, and the rotor speed signal, ω, thereby enabling failsafeoperation of the electric motor system 100 to prevent a vehicle stallcondition.

Referring next to FIG. 4, an exemplary structure of the sensorlessposition and speed estimator 302 is depicted. A low speed errorextraction module 402 and a high speed error module 404 generate a lowspeed error signal and a high speed error signal, respectively. An errorcombining module 406 operates as a speed/position generator to generatethe sensorless position signal 408 and the sensorless speed signal 410for providing to the signal selector 304 (FIG. 3) in response to the lowspeed error signal and the high speed error signal. A sensorlessposition feedback signal 412 is connected to the sensorless positionsignal 408, thereby being equivalent thereto. Likewise, a sensorlessspeed feedback signal 414 is connected to the sensorless speed signal410.

The low speed error extraction module 402 determines the low speed errorsignal in response to the sensorless position feedback signal 412, thesensorless speed feedback signal 414 and the two phase currents(I_(alpha/beta)). In a similar manner, the high speed error module 404determines the high speed error signal in response to the sensorlessposition feedback signal 412, the sensorless speed feedback signal 414,the two phase currents (I_(alpha/beta)) and the two stationary framevoltage commands (V_(alpha/beta)).

The error combining module 406 includes a low speed error phase outmodule 416 and a high speed error phase in module 418 for providing asmooth transition from low speed sensorless operation to high speedsensorless operation. The low speed error phase out module 416 receivesthe low speed error signal and the sensorless speed feedback signal tocalculate a low speed error component value by phasing out the low speederror signal as the speed of the motor increases in response to thesensorless speed feedback signal and a predetermined phase-outcoefficient. Similarly, the high speed error phase in module 418receives the high speed error signal and the sensorless speed feedbacksignal to calculate a high speed error component value by phasing in thehigh speed error signal as the speed of the motor increases in responseto the sensorless speed feedback signal and a predetermined phase-incoefficient. The predetermined phase-out coefficient is selected so thatthe low speed error component value is equal to the low speed errorsignal at near zero speeds and smoothly phases out (e.g., straight-linephase out) to where the low speed error component value is zero when thespeed reaches a predetermined low-to-high-speed transition speed. In alike manner, the predetermined phase-in signal is selected so that thehigh speed error component value is equal to zero at near zero speedsand smoothly phases in (e.g., a straight-line phase in) to where thehigh speed error component value is equal to the high speed error signalwhen the speed reaches or exceeds the predetermined low-to-high-speedtransition speed. An error signal summer 420 combines the low speederror component value and the high speed error component value togenerate a rotor error position signal. A speed observer module 422receives the rotor position error signal and, in response thereto,calculates the sensorless position signal 408 and an observed speedsignal, the observed speed signal being filtered by a speed filter 424to generate the sensorless speed signal 410.

A low speed injection module 426 generates the injected voltagecommands, V_(α) _(—) _(inject) and V_(β) _(—) _(inject), as low speedinjection signals 118 for providing to the summers 214, 216 (FIG. 2) atstartup of the electric motor system 100 and at near zero low speeds toinject a high frequency signal into the flux axis of the permanentmagnet motor 102 for operation of the low speed extraction module 402.The injected voltage commands, V_(α) _(—) _(inject) and V_(β) _(—)_(inject), are generated in response to an injected voltage, V_(inj),which is calculated in accordance with Equation (1).V _(inj) ≡V ₀ −V* _(inj) _(—) _(slope)(abs(ω_(r)−ω_(LH))  (1)wherein V₀ is the injected voltage at startup, V*_(inj) _(—) _(slope) isthe slope at which the voltage is decremented or incremented as afunction of motor speed, and the difference (ω_(r)−ω_(LH)) is thedifference between the rotor speed, ω_(r), and low to high speedthreshold, ω_(LH). When the sensorless position feedback signal 210 hasa near-zero value, the low speed injection module 226 generates apredetermined low speed injection signal (V_(alpha/beta) _(—) _(inj))for injecting a high frequency signal into a flux axis of the motor 102at low speeds and provides the predetermined low speed injection signalas voltage signals 118 to the signal summers 214, 216 (FIG. 2) forcombining with the synchronous frame voltage command signals, V*_(α) andV*_(β). The high frequency signal is injected into the flux axis of themotor 102 at low speeds to generate the sensorless speed feedback signal414 and the sensorless position feedback signal 412 at the low speeds.

A low speed polarity detector 430 compares the low speed errordetermined in response to the sensorless position feedback signal 412 tothe two phase currents (I_(alpha/beta)). When the initial rotor positioninformation is determined by the sensorless rotor position and speedestimator 302, it is imperative to differentiate between the positiveand negative D axis (i.e., the rotor magnet north and south poles). Thelow speed polarity detector 430 determines from the low speed error andthe two phase currents (I_(alpha/beta)) whether the sensorless rotorposition signal is properly aligned with the rotor north pole. If thesensorless rotor position signal is not properly aligned with the rotornorth pole, a reset position signal 432 is provided to the speedobserver module 422. In response to the reset position signal 432, thespeed observer module 422 switches the polarity of the sensorless rotorposition signal so that the position signal 408 is correctly alignedwith the rotor position.

In this manner, the sensorless position and speed estimator 302 providesthe sensorless position signal 408, θ, and the sensorless speed signal410, ω, as feedback signals at both low and high speeds. Particularly,the error combining module 406, including the low speed error phase outmodule 416 and the high speed error phase in module 418, provides asmooth transition from low speed sensorless operation to high speedsensorless operation. Referring to FIG. 5, a modal operation diagram 500depicts operation of the sensorless position and speed estimator 302. Atstartup 502, as described above, the low speed injection module 426initiates the calculation of the sensorless position signal 408 and thesensorless speed signal 410. Next, the low speed polarity detect module430 performs the initial polarity detection 504 and corrects thepolarity of the sensorless position signal 408, if necessary. Operationof the sensorless position and speed estimator 302 then proceeds inaccordance with a low speed mode 506 as determined by the low speedextraction module 402. As described above, operation in accordance withthe low speed mode provides an injection Voltage, V_(inj), in accordancewith Equation (1).

Operation in accordance with the low speed mode 506 continues until thespeed exceeds a predetermined low speed upper threshold. When the speedexceeds the predetermined low speed upper threshold, operation of thesensorless position and speed estimator 302 operates in a transitionmode 508, transitioning from the low speed mode 506 to a high speed mode510. Operation in accordance with the high speed mode 510 continuesuntil the speed falls below a predetermined high speed lower threshold,at which point the operation of the sensorless position and speedestimator 302 operates in a transition mode 512, transitioning from thehigh speed mode 510 to the low speed mode 506. Such predetermined highspeed lower threshold could be set at approximately five hundredrevolutions per minute of the motor 102 and such predetermined low speedupper threshold could be set at approximately eight hundred revolutionsper minute of the motor 102.

Thus it can be seen that the error combining module 406 provides lowspeed sensorless rotor position and rotor speed signals when operatingin the low speed mode 506 when the speed is below the predetermined highspeed lower threshold and provides high speed sensorless rotor positionand rotor speed signals when operating in the high speed mode 510 whenthe speed is above the predetermined low speed upper threshold. When thespeed is less than the predetermined low speed upper threshold and morethan the predetermined high speed lower threshold, the error combiningmodule 406 provides transition signals for the sensorless rotor positionand rotor speed signals, the transition signals generated in accordancewith the low speed error phase out module 416 and the high speed errorphase in module 418 to provide a smooth transition 508 from the lowspeed mode 506 to the high speed mode 510 and, likewise, to provide asmooth transition 512 from the high speed mode 510 to the low speed mode506.

While an exemplary construction of the limp home controller 110 has beendepicted in FIGS. 3 and 4, those skilled in the art will realize that alimp home controller 110 which provides rotor position and rotor speedsignals, θ and ω, when a resolver is operating correctly and when aresolver fails can be constructed in any one of a number of differentconfigurations. For example, the limp home controller 106, including thegeneration of the sensorless position signal and the sensorless speedsignal can be enabled in software. Accordingly, FIG. 6 depicts aflowchart 600 of the operation of the limp home controller 110 inaccordance with the present embodiment.

Initially, the limp home controller 110 determines 602 whether theresolver 108 has failed. If the resolver 108 has not failed, the limphome controller 110 determines 604 whether the control mode at startupis a sensorless control mode or a sensor (i.e., resolver 108) basedcontrol mode as selected by a signal from a higher level controllerwhich can make such selection in accordance with predefined parameters.

For sensor based operation, processing first performs 606 ResolverOffset Learning (ROL). ROL involves injecting a high frequency signalinto the motor 102 and defining, in response to the change in theresolver signals, a resolver offset value (e.g., a number of degreesdifferent between the resolver 108 sensed position signal and the angleof the rotor flux in the motor 102). After performing ROL 606, theoperation of the motor 102 is controlled 608 using the sensed rotorposition and rotor speed signals from the resolver 108. During sensorbased operation, sensorless control state variables are initialized andno high frequency signal is injected at low speeds (step 610).Processing then continues to perform steps 608 and 610 in sensed basedoperation until detection 612 of resolver failure.

When resolver failure is detected 612, operation transitions tosensorless control mode and the state machine is reset with thesensorless control state variables (step 614) so that sensorless controlmode can continue operation from the operational state when the resolver108 failed. Next, processing determines 616 whether the currentoperational state is low speed mode 506 or high speed mode 510 (FIG. 5).

If operation is in the low speed mode 616, processing performs aninitial polarity detect 618 to determine if the low speed sensorlessrotor position signal has the correct polarity. After correcting thepolarity of the low speed sensorless rotor position signal if necessary618, operation continues 620 in accordance with the low speed sensorlessmode 506 until the speed of the motor 102 becomes 622 greater than apredetermined low speed upper threshold.

When the speed of the motor 102 becomes 622 greater than thepredetermined low speed upper threshold 622, operation transitions 624to the high speed sensorless mode 510. Operation then continues 626 inaccordance with the high speed sensorless mode 510 until the speed ofthe motor 102 becomes 628 less than a predetermined high speed lowerthreshold. When the speed of the motor 102 becomes 628 less than thepredetermined high speed lower threshold 628, operation returns to step620 for controlling the motor 102 in accordance with the low speedsensorless mode 506.

If at step 616 it is determined that operation of the motor 102 whenfailure of the resolver 108 was detected 612 was in the high speed mode,processing jumps to step 624 to transition into high speed sensorlessmode 510. Further, if at startup the sensorless control mode is selected604, operation starts in the low speed sensorless operation mode byperforming 618 initial polarity detect.

Thus it can be seen that the present method and apparatus for limp homeoperational mode of the electric motor system 100 when the resolver 108fails utilizes position sensorless algorithms to provide a backup formotor controls, thereby providing a limp home operational mode whichallows the driver to safely drive a vehicle with a failed resolver to aservice station. While at least one exemplary embodiment has beenpresented in the foregoing detailed description, it should beappreciated that a vast number of variations exist. It should also beappreciated that the exemplary embodiment or exemplary embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the invention in any way. Rather, the foregoingdetailed description will provide those skilled in the art with aconvenient road map for implementing the exemplary embodiment orexemplary embodiments. It should be understood that various changes canbe made in the function and arrangement of elements without departingfrom the scope of the invention as set forth in the appended claims andthe legal equivalents thereof.

1. A method for operation of an electric motor system comprising:determining whether a resolver has failed; operating the electric motorsystem using resolver signals when the resolver has not failed; anddetermining sensorless signals based on a low speed mode, a high speedmode and a transition mode; and operating the electric motor systemusing the sensorless signals when the resolver has failed.
 2. The methodin accordance with claim 1 wherein the resolver signals comprise signalsgenerated in response to a rotor position and a rotor speed of a rotorof an internal permanent magnet motor of the electric motor system. 3.The method in accordance with claim 1 wherein the sensorless signalscomprise signals corresponding to a rotor position and a rotor speed ofa rotor of an internal permanent magnet motor of the electric motorsystem.
 4. The method in accordance with claim 3 wherein the sensorlesssignals comprise a high speed sensorless rotor position signal and ahigh speed sensorless rotor speed signal.
 5. The method in accordancewith claim 3 wherein the sensorless signals comprise a low speedsensorless rotor position signal and a low speed sensorless rotor speedsignal.
 6. The method in accordance with claim 5 wherein the sensorlesssignals further comprise low speed injection signals.
 7. The method inaccordance with claim 4 wherein the sensorless signals further compriselow speed sensorless rotor position and rotor speed signals, and whereinrotor position and rotor speed signals transition from the high speedsensorless rotor position and rotor speed signals to the low speedsensorless rotor position and rotor speed signals in response to a speedof the internal permanent magnet motor becoming less than apredetermined high speed lower threshold value.
 8. The method inaccordance with claim 7 and wherein the rotor position and rotor speedsignals further transition from the low speed sensorless rotor positionand rotor speed signals to the high speed sensorless rotor position androtor speed signals in response to the speed of the internal permanentmagnet motor becoming more than a predetermined low speed upperthreshold value.
 9. A limp home controller for controlling operation ofan internal permanent magnet motor, the limp home controller comprising:a sensorless speed and position estimator for generating sensorlessrotor position and rotor speed signals based on a low speed mode, a highspeed mode and a transition mode; and a signal selector coupled to aresolver for receiving sensed rotor position and rotor speed signalstherefrom and coupled to the sensorless speed and position estimator forreceiving the sensorless rotor position and rotor speed signalstherefrom, the signal selector determining whether the resolver hasfailed and providing the sensed rotor position and rotor speed signalsfor controlling the operation of the internal permanent magnet motorwhen the resolver has not failed and providing the sensorless rotorposition and rotor speed signals for controlling the operation of theinternal permanent magnet motor when the resolver has failed.
 10. Thelimp home controller in accordance with claim 9 wherein the signalselector includes a resolver failure detector coupled to the resolverfor receiving the sensed rotor position and rotor speed signalstherefrom and determining in response to the sensed rotor position androtor speed signals whether the resolver has failed.
 11. The limp homecontroller in accordance with claim 9 wherein the sensorless speed andposition estimator generates high speed sensorless rotor position androtor speed signals in response to a speed of the internal permanentmagnet motor being greater than a first predetermined speed.
 12. Thelimp home operation controller in accordance with claim 11 wherein thesensorless speed and position estimator also generates low speedsensorless rotor position and rotor speed signals in response to thespeed of the internal permanent magnet motor being less than a secondpredetermined speed.
 13. The limp home operation controller inaccordance with claim 12 wherein the sensorless speed and positionestimator further generates low speed injection signals for control ofthe operation of the internal permanent magnet motor in response to thespeed of the internal permanent magnet motor being less than the secondpredetermined speed.
 14. The limp home operation controller inaccordance with claim 12 wherein the sensorless speed and positionestimator generates transition signals in response to the speed of theinternal permanent magnet motor being less than the first predeterminedspeed and more than the second predetermined speed.
 15. An electricmotor system comprising: an internal permanent magnet motor comprising aplurality of phases and including a rotor; an inverter for generating aplurality of phase signals in response to modulated control signals andcoupled to the internal permanent magnet motor for providing each of theplurality of phase signals to a corresponding one of the plurality ofphases of the permanent magnet motor; an inverter controller forgenerating the modulated control signals in response to a rotor positionsignal, a rotor speed signal and phase current signals, the phasecurrent signals corresponding to currents of one or more of theplurality of phase signals; a resolver coupled to the internal permanentmagnet motor for sensing a position and movement of the rotor, theresolver generating sensed rotor position and rotor speed signals inresponse to the position and the movement of the rotor; and a limp homecontroller coupled to the resolver and the inverter controller thatdetermines whether the resolver has failed and, when the resolver hasnot failed, provides the sensed rotor position and rotor speed signalsto the inverter controller as the rotor position signal and the rotorspeed signal, and when the resolver has failed, determines sensorlessrotor position and rotor speed signals based on a low speed mode, a highspeed mode and a transition mode and provides the sensorless rotorposition and rotor speed signals generated by the limp home controllerto the inverter controller as the rotor position signal and the rotorspeed signal.
 16. The electric motor system in accordance with claim 15wherein the limp home controller comprises: a sensorless speed andposition estimator for generating the sensorless rotor position androtor speed signals; and a signal selector coupled to the resolver forreceiving the sensed rotor position and rotor speed signals therefromand coupled to the sensorless speed and position estimator for receivingthe sensorless rotor position and rotor speed signals therefrom, thesignal selector determining whether the resolver has failed andproviding the sensed rotor position and rotor speed signals to theinverter controller as the rotor position signal and the rotor speedsignal when the resolver has not failed and providing the sensorlessrotor position and rotor speed signals to the inverter controller as therotor position signal and the rotor speed signal when the resolver hasfailed.
 17. The electric motor system in accordance with claim 16wherein the signal selector includes a resolver failure detector coupledto the resolver for receiving the sensed rotor position and rotor speedsignals therefrom and determining in response to the sensed rotorposition and rotor speed signals whether the resolver has failed. 18.The electric motor system in accordance with claim 16 wherein thesensorless speed and position estimator comprises a high speed errorcalculator for determining a high speed error signal in response to theplurality of phase signals, a sensorless position feedback signal, and asensorless speed feedback signal.
 19. The electric motor system inaccordance with claim 18 wherein the sensorless speed and positionestimator further comprises a low speed error calculator for determininga low speed error signal in response to the plurality of phase signals,the sensorless position feedback signal, and the sensorless speedfeedback signal.
 20. The electric motor system in accordance with claim19 wherein the sensorless speed and position estimator furthercomprising an error combiner coupled to the high speed error calculatorand the low speed calculator for determining the sensorless positionsignal and the sensorless speed signal in response to the high speederror signal and the low speed error signal, wherein the sensorlessposition feedback signal is equivalent to the sensorless position signaland the sensorless speed feedback signal is equivalent to the sensorlessspeed signal.